Viscoelastic characterization of angle ply advanced composites

Abstract

Time dependent properties of angle ply laminated Boron/Epoxy and Graphite/Epoxy fiber controlled composites were investigated. The main objective of this study was to develop a technique to establish interconversion of different test results using appropriate viscoelastic theory to formulate an accelerated testing procedure.

To achieve this aim, forced vibration, constant strain rate and creep tests were performed at different temperature levels. Due to its practical importance, behavior below the glass transition temperature was studied. Multiple regression techniques were used to generate response surfaces for significant variables. Master curves using the time-temperature superposition principle were established for individual tests. Mechanical model representation, integral equation formulation and numerical integration methods based on linear viscoelasticity were used to predict constant strain rate and long time creep behavior of composites from nondestructive short time dynamic tests.

It has been shown that a regression equation and its constants can be conveniently used to obtain horizontal and vertical shift and also to perform viscoelastic analysis. While time-temperature superposition can be applied to each test its validity in general needs further study. Simple mechanical models fail to predict constant strain rate tests. Constant strain rate and creep tests were predicted using measured damping ratios and storage moduli from dynamic tests. Also, relaxation moduli were obtained over eleven decades of time scale from different tests. Thus, applicability of linear viscoelastic theory to predict the gross behavior of these composites is established.